Sound signal transmitter device



April 23, 1957 E. o. OBERG 2,790,164

SOUND SIGNAL TRANSMITTER DEVICE Filed Dec. 2, 1954 2 Sheets-Sheet 1INVENTOR BY IZQBQM;

ATTORNEY United StatesPatentfO ce 2',790-,1-64 SOUNDLSIGNALTRANSMITTERDEVTCE mEI'ik Ot'filberg; laidingo," Sweden; assignor :toSvehska Aktieboiaget Gasaceumulator, Lidingo, Sweden, acorporation ofSweden -Appiication 'December 2," 1954 Serial'No 472;7 50 Claimspriority; application Sweden-April's, 1 954- scams. or. amazes rAssoundsignal transmitters especially adapted for beazc'onsiandsimilarnavigatory'means of assistance are nowadays chiefly usedelectromagnetic sound 'sigrial transmiters 2 according to the telephoneprinciple? These usu'ally .7 on-tain a weak iron-core provid'ed withawindi-ngy 'said ufwinding influencing a diaphragmor eventu'ally adiaplaces within the transmitter. It has been proposed to meltz thesaidice bark or show i bark away by meansof electricheater eo'ils', but theexp'eriences" hitherto made have had no success in this respect.

The present invention is based upon-an'investigation Labout thecurrents'of air present in 'the exponential horn "of a sound transmitterof theabove mentioned kind; and

of the' elimaticoccurrences in the sound signah transmitt'er;respectively; determining theplacebf'forniation of the'ice barkor'thesnow bark; 'andtheinvent ion' refers '---to anarrangement=based-onthese theoreticaltinvestigations, by which one caneffectively prevent theformation of detrimental snowbarker icebark. I J

The inventionisfurther described. in connectionf'with I Tithe attacheddrawings, which show a sound signal trai'nsmitten'of the presen't kindat two difierent occasions,

Fig; 1 3 shows a sound signal" transmitterwithou tthe ater eoil of thepresent'invention. Fig? 2" shows a soundsignal transmitter utilizihg theheater coil and 'cor're'sponding'electricahnetworks.

n the drawingstheweakiron core isrindicated 10, andthewihdingsurrounding said-went iron'core, which is fed by alternatingciirrent ofaudio-"frequency is indicated-11. The weakironcoreiSwinI'thiS ca'setassumed alto be linear; and consequentlyonechasappliedaneupper" diaphragm 12 and a lower diaphragm 13 opposite to eachend of the core 16. The magnetic circuit is completed through a casing14, which is arranged between the diaphragms. The diaphragms are clampedin place by means of clamping rings 15, and outside these clamping ringslids 16 are provided, said lids being combined with the exponentialhorns 17.

As snow bark and ice bark have substantially the same influence in therespects here in question they will be 'indicated below as bark withoutany difierence being made between them. The experience has now provedthat bark appears in the opening of the two exponential horns, howeverusually to a greater extent in the upper exponential as indicated at 18,and to a less extent at the lower exponential horn, as indicated at 19.Furthermore, bark usually also forms on the upper diaphragm 12, asindi-r .rphragm applied at each'end 'of' the rod=formedcore; he'

30 v *Investigations fof 50 "independently thereof the" ibrationsof the2,790,164 Paeented Axpri zli, 1 957 earl i a t, t. It has proved,however; that h s is usually no he i'case. T-he' opening=21*wliichforrny thesour i sound' transmitter wt a ra we i $i bfi neat we median g'ger;so*smtill;;liowever, thatanessential tlecrease'otthe power 0 the soundansmitter occurs just ori that"occasion whenfthetran' m ssion from thesouhd transinitter is of the"greatest"in v The formation 29 of barkcauses further anurre a vload s0und"transmittei" is'put out'i'offuntionxf It'is therefore fbark fis1ffornied, but'these'trials havehitherto 1 given no "goodd'e'sults. The freason forthis is assumed tobethat m-has; "not"tak'en' sufficient Yregard'to the aircirculation'"conditionsfemanating' in fan exponential'horn".oftheilkind "There inquestion i v pg the basis tithepate -i sen- *ftion, as ai'matteriofifacthave provedthe followingrelav I of'coinpressihility of the iairif thatmeansthefcharacter stic'stating the compression pressure 1'iof the *airas a'function of 'foriinstancelthe' moveme t of These two circulations.ofi air are 'superposed'on :eaeh ibthergf and they-:f'o'llowsubstantially "F the same. lawsffwh h" also exist in radio Itechnic'rectificatibn,in which a directlcur reht is created the rectification,but in whichth'reiisf'siiperposedon,this direct ourrent r a "re'st entoffth'e: high frequency currency.

' v ,raphragms 312 andflgi isthe'higjgest'in"'the middle pa r-'tfa'ndjconsequently you "will'obcesr'reetificatieaiefiect ndthe strongestipresusing 2;: rec ified current of air indirection Qua/ads n the centreof the diaphragms,

. ,r i i i fi a "finia sound transmittefot j the type here in questionare v l1'aiiges3wliich e'asily eatrse a rather "st iongheatingof the air." abe -provided: direetrenar pntentialanus coop'erates at least in theupper exponential horn 17 with the produced heat potential for providingcurrent of ventilation. This current of ventilation will for the reasonsmentioned above take place in the direction of the arrow 23 when therewill be a created ventilation current also in the lower 7exp'onential'horn 17, even if this current isweaker, as v indicated bythe shorter arrow 24. In both cases the ventilation current follows thelaws, which are wellknown as far as regards directional air currentssuperposed" 0 on sound waves. These laws mean that the current of air isto a very high degree ofexactness directed perpendicularly to theisobars representing the sound wave The purpose of the exponential hornsis now that the sound wave should be propagated as far as possible alongisobars running perpendicularly to the centre line 25 of the exponentialhorn. The consequence thereof is also that the outward directedventilation current will rather exactly follow the centre line, however,spreading itself out across the isonode planes, and consequently theinward directed ventilation current for replacing the outward directedcurrent will be forced to accept a current way, which closely followsthe wall of the exponential horn as a surface current.

The invention is now based on two ditferent conditions, viz that oneshall by causing a suitable resistance to the ventilation currentdecrease this current as' far as possible, and further, that one shallby the provision of heater elements in the way of the ventilationcurrent provide for the air, fed to the interior of the exponentialhorn, as far as possible being so hot, that formation of bark isavoided. V

The provision of resistors in the way of the ventilation current will ofcourse also mean that one provides a resistor in the way of the soundwave, and this is unfavourable for the function of the soundtransmitter. However, practical tests have proved that the sound wave isdue to the friction resistance against the wall of the sound hornpropagating only to a very small extent through the surface layer, wherethe inward directed component of the ventilation current is passing, asis stated above. If the heating means'are nowplaced very close to thewall of the sound horn, they will create unincreased resistance to theventilation current without thereby appreciably damping the sound waves.Thus one will in this way obtain a resistance, eventually initiated by awhirl formation at the heater means and thereby essentially improved, asfar as regards the ventilation current, without said resistancealfecting the sound-carrying air current. It is thus evident from theabove that the heater means should be placed close to the wall of theexponential horn, so that they heat and brake the inwarddirectedreplacement ventilation current eventually under formation ofwhirls. They partly decrease the ventilation current, and, thereby alsocause decreased cooling of the interior of the exponential horn, partlyalso heat the replacementair, which is slipping inwards along the wallsof the exponential horn, and in this way one isforcing a rather hightemperature of the air in the interior of the exponential horn.

' Placing now the heater. coil substantially vertically or 'in'any casesubstantially perpendicularly to the direction line 25 rather close tothe opening of the exponential horn, one will further gain that theoutward directed radiation from the heat coil will be sutlicient formelting down the bark 18, at the same time as transferring heat 4 of theheater coil 28. Thereby the resistance against inwardly directed aircurrent will be further increased as compared with the direct currentresistance provided by the heater coil 28.

Practical tests have proved that one can with a rather low power on theheater coil 28 achieve a complete debarking of sound signal transmittersof the type here in question also during the most severe climaticconditions. The power, as a matter of fact, must not be greater thanabout the half of the power fed to the coil 11 for creating the soundwave. For decreasing the total maximal power in a system of the presentkind one therefore advantageously provides the heater coil 28 and thewinding 11 to operate alternatively. This will take place according tothe invention in such a way, that power is fed from the network 30 to acoupling arrangement 31, controlled by a pulse mechanism 32. The pulsemechanism 32, in time with the sound pulse which should be transmittedfrom the sound transmitter, combines the network with conductors runningto an audio-frequency converter 33, converting the input electricalpower into audio frequency power, said power being fed through theconductors 34 to the winding 11 in the sound transmitter. During theperiods, when the electrical power is not transferred to the frequencyconverter 33, it is instead over conductors 35 transferred to the heatercoils 28. The heater coils 28 are thus intermittently heated, but theyshould suitably have so great heat capacity, that they are'not f-ullycooled during the time, when the sound transmission is taking place. Theheat present in the heater coil 28 will thus perhaps vary intemperature, but it will anyhow under all circumstances be sufficientfor maintaining the abovementioned function regarding the ventilationcurrent, by which formation of bark in the sound transmitter isefiectively prevented.

The invention, of course, is not limited to the arrangement abovedescribed in detail, but difierent modifications m-ay be made within theframe of the invention.

What is claimed is: 1. An outdoor sound transmitter comprising anexponentially formed horn open at one end, a diaphragm I at the otherend of said horn, means for vibrating the diaphragm, and an electricallyheated toroidal heater coil disposed immediately inside the open end ofsaid horn, said heater coil preventing the formation of ice and snowdeposits within the horn by heating the cold input air. r

2."An outdoor sound transmitter according to claim 1 wherein saidvibrating means and 'the heater coil are connected to a single source ofelectric current and are intermittently energized'from said singlecurrent source 7 through an intermittently acting switching means.

by convection to the air moving inwards, saidheat being I suflicient formelting down the bark part 20. In the cases, when the inward movingcurrent of air is forced into a whirl formation by the heat coil, asindicated by the dotted line 26, this whirl 27 will of course haveradial deepness from the surface of the wallet the exponential horn,which is esesntially greater than the radial deepness wherein the heatercoil :is mounted in lar to the center line through said he 3; An outdoorsound transmitter according to claim 1 a plane perpendicustreams Citedin the file ofthis patent UNITED STATES PATENTS I Wm "ran. 18, 1927Soderberg Oct. 9, 1945

